Subview added but lost part of drawing?

Question

I want to draw a custom UIButton with 'add' surface and UIBlurEffect background. I override the drawRect method in the surface view:

class SurfaceAdd: UIView {
    override func drawRect(rect: CGRect) {
    var currentContext = UIGraphicsGetCurrentContext()
    CGContextSaveGState(currentContext)
    //draw circle
    CGContextAddEllipseInRect(currentContext, self.bounds)
    CGContextSetRGBFillColor(currentContext, 0, 0, 0, 0.2)
    CGContextFillPath(currentContext)

    CGContextRestoreGState(currentContext)
    CGContextSetLineCap(currentContext, kCGLineCapRound)
    CGContextSetLineWidth(currentContext, 8)
    CGContextSetRGBStrokeColor(currentContext, 1, 1, 1, 1)
    let height = self.frame.size.height
    let width = self.frame.size.width
    //draw +
    CGContextSetShadow(currentContext, CGSizeMake(1, 1), 0)
    CGContextMoveToPoint(currentContext, width*0.25, height/2)
    CGContextAddLineToPoint(currentContext, width*0.75, height/2)
    CGContextMoveToPoint(currentContext, width/2, height*0.25)
    CGContextAddLineToPoint(currentContext, width/2, height*0.75)
    CGContextStrokePath(currentContext)
}

It looks nice when I use it as a separate UIView in the storyboard.
However, when i add it as a subview of my custom UIButton, and then add the custom button in storyboard, the ellipse disappear and the background turns black.

relevant code in CustomButton here:

var iconAdd:SurfaceAdd!
override init() {
    super.init()
    setup()
}

required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    setup()
}
private func setup(){
    self.iconAdd = SurfaceAdd(frame: self.bounds)
    self.addSubview(iconAdd)
    self.setNeedsDisplay()
}

What's wrong with me?

ps:I choose to use constraints for layout, for now I just use frame to have a test. So, please don't mention mistake about that.

Answer 1

You should set its background color as clear color before it being added to another view, otherwise, it will look like it has a black background color.

self.iconAdd.backgroundColor = UIColor.clearColor()